There are many operations downhole that require circulation or reverse circulation through a tool string. Almost as often the circulation valve needs to be operated between two positions so that, for example, it can be run in open to the desired location and then after the circulation is done, it can be closed again.
There are many types of circulation valves that are in use downhole. Some have an internal ported sleeve that is attached to a housing with a port through a j-slot mechanism. With this type of valve picking up and setting down weight gets the ports aligned or misaligned, as needed. These types of valves are less suitable for deviated wellbores where it is difficult to know if picking up and setting down has actually shifted the circulation valve or merely stretched the tubing string from a location near a wellbore deviation.
Other types of circulation valves involve the use of ever larger balls to move a circulation valve between its end positions. This design allows an initial smaller ball to land on a seat to pressure up to set another tool followed by a further pressure to move the valve to another position. In order to move the valve again to its initial position a bigger ball has to land on a bigger seat to, for example, shift a different sleeve. The initial ball is typically released as its seat shifts into a recess and opens up. Such seats can be made of collet segments that are held together in an initial position to allow pressure buildup on a seated ball and then the collet fingers in a groove can spread apart allowing the ball to go on through.
As an alternative, a different seat has been employed that simply enlarges as the ball is blown though it with pressure. It then stands ready to receive another ball that is larger for another operation.
A circulation valve with disappearing balls has been offered. The idea here is to use a seat that keeps its dimension so that it can accept a constant ball size. The idea is that the ball lands on the seat and permits whatever operation is needed and then just goes away from exposure to well conditions over time. The problem with this design is that the balls are rather soft and are prone to be eroded during delivery or even when on the ball seat itself and before the operation that depends on the ball sealing can be accomplished.
Other issues that have affected ball seats made of a series of collets is that the sealing happens on a series of abutting shoulders and in a downhole environment where debris can settle on the seating surface and reduce the chance for a good seal on the ball.
The present invention seeks to overcome some of these disadvantages. While the invention is presented in the context of a circulation valve it can be deployed in other applications downhole. These and other advantages of the present invention will become more apparent to those skilled in the art from a review of the preferred embodiment described below along with its associated drawings while recognizing that the claims define the full scope of the invention.